Dielectric film with low coefficient of thermal expansion (CTE) using liquid crystalline resin

ABSTRACT

An embodiment of the present invention is a technique to provide a dielectric film material with controllable coefficient of thermal expansion (CTE). A first compound containing a first liquid crystalline component is formed. The first compound is cast into a first film. The first film is oriented in an magnetic or electromagnetic field in a first direction. The first film is cured at a first temperature.

BACKGROUND

1. Field of the Invention

Embodiments of the invention relate to the field of semiconductor, andmore specifically, to semiconductor materials.

2. Description of Related Art

The next generation die interlayer dielectric (ILD) materials are porousand have poor mechanical strength. To reduce the stresses on the ILD dueto coefficient of thermal expansion (CTE) mismatches between materialsin the package, low CTE materials are needed. In addition, due to theneed for materials to flow over greater distances through narrower gaps,there is a need to eliminate, or minimize the concentration of, thefiller, which is typically used to reduce the CTE.

Existing techniques to reduce the CTE and at the same time reduce oreliminate the concentration of the filler has a number of disadvantages.One technique increases the cross-link density and/or increases thefiller loading of the dielectric material. This technique leads to highmodulus and high viscosity, resulting in cohesive and adhesive failuremodes.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention may best be understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the invention. In the drawings:

FIG. 1A is a diagram illustrating a semiconductor device in which oneembodiment of the invention can be practiced.

FIG. 1B is a diagram illustrating a semiconductor package according toone embodiment of the invention.

FIG. 2 is a diagram illustrating a structure of the dielectric materialaccording to one embodiment of the invention.

FIG. 3 is a diagram illustrating another structure of the dielectricmaterial according to one embodiment of the invention.

FIG. 4 is a flowchart illustrating a process to provide the dielectriclayer according to one embodiment of the invention.

FIG. 5 is a diagram illustrating an epoxy resin according to oneembodiment of the invention.

DESCRIPTION

An embodiment of the present invention is a technique to provide adielectric film material with controllable coefficient of thermalexpansion (CTE). A first compound containing a first liquid crystallinecomponent is formed. The first compound is cast into a first film. Thefirst film is oriented in an magnetic or electromagnetic field in afirst direction. The first film is cured at a first temperature.

In the following description, numerous specific details are set forth.However, it is understood that embodiments of the invention may bepracticed without these specific details. In other instances, well-knowncircuits, structures, and techniques have not been shown to avoidobscuring the understanding of this description.

One embodiment of the invention may be described as a process which isusually depicted as a flowchart, a flow diagram, a structure diagram, ora block diagram. Although a flowchart may describe the operations as asequential process, many of the operations can be performed in parallelor concurrently. In addition, the order of the operations may bere-arranged. A process is terminated when its operations are completed.A process may correspond to a method, a procedure, a method ofmanufacturing or fabrication, etc.

One embodiment of the invention is to provide a dielectric material withcontrollable coefficient of thermal expansion (CTE). The CTE may becontrolled to be from a small negative value to over 100 ppm/° C. bycontrolling (1) the amount of liquid crystal resin in the formulation,and (2) the extent to which the liquid crystalline resin is oriented.The material technology addresses the current low CTE need and may bescalable to future packages with ultra low CTE requirements. Inaddition, since the elastic modulus of a liquid crystal resin is muchreduced in angles other than perpendicular to the direction oforientation, the dielectric film exhibits low modulus in the z-directionto become resilient with respect to mechanical stability problems causedby package motion.

One embodiment of the invention provides dielectric materials that areuseful for a number of applications. Examples of these applicationsinclude: (1) traditional substrate build-up processes involving copperplating, photo resist lamination, exposure, development, etching, andresist removal, (2) photo definable dielectric films (without the use ofa photo resist), (3) printed circuit board (PCB) fabrication and (4)imprinting.

FIG. 1A is a diagram illustrating a semiconductor device 100 in whichone embodiment of the invention can be practiced. The semiconductordevice 100 includes a substrate layer 110 and two dielectric layers 120and 130.

The substrate layer 110 is any suitable semiconductor substrate such assilicon. During the fabrication process, device elements such as fieldoxides, sources and drains are formed on the substrate.

The dielectric layer 120 is deposited on the substrate layer 110. Otherlayers such as metal interconnect, gates may be deposited as part of atypical semiconductor fabrication process. The dielectric layer 120 mayinclude a single film or multiple films. As illustrated in FIG. 1A,three films 122, 124, and 126 form the dielectric layer 120. Each of thefilms 122, 124, and 126 may have a different CTE at a selected magneticfield direction.

The dielectric layer 130 is formed below the surface of the substratelayer 110. It may be optional and may provide additional protection orother functionalities Like the dielectric layer 120, the dielectriclayer 130 may include a single film or multiple films. As illustrated inFIG. 1, it includes three films 132, 134, and 136 Like in the dielectriclayer 120, each of the films 132, 134, and 136 may have a different CTEat a selected magnetic field direction.

Any one of the dielectric layers 120 and 130 is constructed according toone embodiment of the invention to have controllable CTE. The CTE may beprovided with low values. The multiple films in each of the layers 120and 130 are oriented in different directions in a magnetic orelectromagnetic field with suitable magnetic strength, time,temperature, and orientation of the magnetic field. By selecting propervalues for the magnetic field strength, time, temperature, andorientation, controllable CTE values may be achieved. The film is formedby a compound or material that comprises monomers having a generalstructure as shown in FIGS. 2 and 3.

FIG. 1B is a diagram illustrating a semiconductor package 140 accordingto one embodiment of the invention. The package 140 is a flip chippackage. However, it is contemplated that any other type of package mayalso be used. The package 140 includes a package substrate 145 and a die150.

The package substrate 145 is any suitable package substrate, ceramic ororganic, such as standard FR4, high graded epoxy (e.g., bismaleimidetriazine) and flexible circuit substrate. The package substrate 145typically has a low coefficient of thermal expansion (CTE). The die 150is any semiconductor die. It includes an integrated circuit (e.g.,processor, memory), a device, components, etc. The underfill 155 is anadhesive to join the entire surface of the chip to the substrate. It istypically an epoxy.

The die 150 has bumps 160. Any suitable type of bumps may be used suchas Controlled Collapse Chip Connection (C4), plated bumps, stud bumps,etc. The bumps 160 provide electrically and thermally conductive pathsto the substrate 145. They also serve to provide part of the mechanicalmounting of the die to the substrate 145 and act as a short lead torelieve the mechanical strain between the substrate and the board.

The substrate 145 includes a dielectric layer 165, traces and vias 170,and a substrate core 175. The dielectric layer 165 has a controllableCTE to match with the substrate core 175 provided by one embodiment ofthe invention. The traces and vias 170 provide contacts and electricalpaths to the substrate. The substrate core 175 may be made of anysuitable material such as epoxy.

FIG. 2 is a diagram illustrating a structure 200 of the dielectricmaterial according to one embodiment of the invention.

The structure 200 includes a liquid crystalline segment 210, twoelements X 222 and 224, and (CH₂)n. The liquid crystalline segment 210is a rod-like liquid crystalline component. Each of the two elements X's222 and 224 is independently selected from a group of oxygen, carbonyl,carboxyl, oxycarbonyl, and amine. The integer n in (CH₂)n is between 1and 20. The monomer formed by the structure 200 has a melting point ofbelow approximately 200° C.

FIG. 3 is a diagram illustrating another structure 300 of the dielectricmaterial according to one embodiment of the invention.

The structure 300 includes a liquid crystalline segment 310, twoelements X 322 and 324, (CH₂)n, and two elements Y's 332 and 334. Theliquid crystalline segment 310 is a rod-like liquid crystallinecomponent. Each of the two elements X's and Y's 322, 324, 332, and 334is independently selected from a group of oxygen, carbonyl, carboxyl,oxycarbonyl, and amine. The integer n in (CH₂)n is between 2 and 20. Themonomer formed by the structure 300 also has a melting point of belowapproximately 200° C.

The dielectric materials formed by the structures 200 and 300 may alsobe added with additives such as solvents, one or more catalysts, one ormore fillers, and other additives such as adhesion promoters, moldrelease agents, colorants, stabilizers, flame retardants, and the likeadditives as known by one skilled in the art.

In one embodiment of the invention, the dielectric material as formedabove is cast into a film and oriented by a magnetic or electromagneticfield, and then used to prepare as substrate. It is also useful toemploy a solvent as diluent to aid film formation and orientation of theliquid crystal resin.

In another embodiment of the invention, the dielectric material is castinto a film, laminated onto a substrate, oriented by a magnetic orelectromagnetic field while curing at elevated temperature, typicallyabove the melting point of the resin, and then used to prepare asubstrate. The magnetic or electromagnetic orientation of the dielectricfilm may be conducted on the cast film, prior to drying any solventused, and during cure. The extent of liquid crystal resin orientation,which affects the CTE properties, is controlled by the magnetic orelectromagnetic strength, time, temperature, and orientation of themagnetic or electromagnetic field.

The dielectric layer may also include a number of dielectric films asshown in FIG. 1. The dielectric films include the liquid crystal resinformed as above with different orientation directions and/or todifferent extents to provide desired two or three-dimensionalproperties. For example, three films may be used and oriented in thex-direction, the y-direction, and the z-direction.

FIG. 4 is a diagram illustrating a process 400 to provide the dielectriclayer according to one embodiment of the invention.

Upon START, the process 400 forms a compound containing a liquidcrystalline component (Block 410). The compound has the structure asshown in FIGS. 2 and 3. Next, the process 400 casts the compound into afilm (Block 420). Then, the process 400 orients the film in a magneticor electromagnetic field in a direction k (Block 430). The direction kmay be the x-direction, the y-direction, or the z-direction as desired.

Next, the process 400 cures the film at a temperature (Block 440). Thistemperature is typically higher than the melting point of the resin,e.g., above 200° C. Then, the process 400 laminates the film on asubstrate or on another film as appropriate (Block 450). Next, theprocess 400 determines if an additional layer is desired (Block 460). Ifso, the process 400 goes back to Block 410 to repeat the process withthe same or different magnetic strength, time, temperature, andorientation. Otherwise, the process 400 is terminated.

Experiments are conducted to provide quantitative data for thedielectric material described above. The experiments are conducted withand without magnetic or electromagnetic orientation, and with andwithout fillers. The results confirm that controllable CTE's areachieved in different directions of the orientation.

In the first experiment, a dielectric film is formed without magnetic orelectromagnetic orientation. A mixture is formed by 210 parts of methylethyl ketone, 20 parts of digylcidyl Bisphenol-A, 20 parts of tetrabromoBisphenol-A, 20 parts of ortho-cresol novolak epoxy resin (215 g/eq), 15parts of epoxy-terminated polybutadiene rubber, 50 parts of brominatedphenolic novolak resin, 4 parts of2,4-diamino-6-(2-methyl-1-imadizolylethyl)-1,3,5-triazine.isocyanuricacid adduct, and 11 parts of silica (maximum particle size of 5microns). These components are added to a planetary mixer, heated toabout 80° C., and mixed at 50 revolutions per minute (rpm) for about onehour. The mixture is then passed twice through a 2-roll mill at about80° C. The above mixture is cast onto 40 micron thick Mylar film anddried at about 100° C. for 15 minutes to provide a total film thicknessof about 70 microns. The film is then laminated onto a substratematerial by vacuum lamination at about 120° C. and 1 torr. The film iscured at about 170° C. for 2 hours. The dielectric layer thus preparedhas CTE of about 65 ppm in the x,y-plane of the film and in thez-direction.

In the second experiment, the procedure described in the firstexperiment is repeated except that while curing the multilayerstructure, a magnetic field of about 0.3 Telsa is applied. Thedielectric layer thus prepared has CTE of about 80 ppm in the x,y-planeof the film and about 40 ppm in the z-direction. This experiment showsthat the CTE of each film at a different orientation may be controlledto be different. Furthermore, low values of CTE (e.g., 40 ppm) may alsobe achieved.

In the third experiment, a mixture is formed by 210 parts of methylethyl ketone, 60 parts of an epoxy resin B (shown in FIG. 5), 20 partsof ortho-cresol novolak epoxy resin (215 g/eq), 15 parts ofepoxy-terminated polybutadiene rubber, 50 parts of brominated phenolicnovolak resin, 4 parts of2,4-diamino-6-(2-methyl-1-imadizolylethyl)-1,3,5-triazine.isocyanuricacid adduct, and 11 parts of silica (maximum particle size of 5microns). These components are added to a planetary mixer, heated toabout 80° C., and mixed at 50 rpm for about 1 hour. The mixture is thenpassed twice through a 2-roll mill at about 80° C. The above mixture iscast onto 40 micron thick Mylar film. The film is placed into a magneticfield of about 0.3 Telsa in the z-direction for 30 minutes, and thendried at about 100° C. for 15 minutes in the magnetic field to provide atotal film thickness of about 70 microns. The film is then laminatedonto a substrate material by vacuum lamination at about 120° C. and 1torr. The film is cured at about 170° C. for 2 hours. The dielectriclayer thus prepared has CTE of about 75 ppm in the x,y-plane of the filmand about 50 ppm in the z-direction.

In the fourth experiment, the procedure described in the thirdexperiment is repeated except that no fillers are used. The dielectriclayer thus prepared has CTE of about 125 ppm in the x,y-plane of thefilm and about 5 ppm in the z-direction. This experiment illustratesthat without fillers, very low CTE values (e.g., 5 ppm) may be achievedat a selected orientation or direction.

FIG. 5 is a diagram illustrating the epoxy resin B according to oneembodiment of the invention. This epoxy resin B is used in the thirdexperiment to produce the mixture.

While the invention has been described in terms of several embodiments,those of ordinary skill in the art will recognize that the invention isnot limited to the embodiments described, but can be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

What is claimed is:
 1. A semiconductor package comprising: a siliconsubstrate layer; a dielectric layer disposed over the silicon substratelayer, the dielectric layer comprising a first film formed from a firstcompound containing a first liquid crystalline component and a secondfilm formed from a second compound containing a second liquidcrystalline component, wherein the first film is oriented in a firstdirection and the second film is oriented in a second direction thesecond direction different and not orthogonal to the first direction,wherein the dielectric layer has a coefficient of thermal expansion(CTE) that matches with the CTE of said silicon substrate layer.
 2. Thesemiconductor package of claim 1 wherein the first film comprises: atleast an additive added to the compound.
 3. The semiconductor package ofclaim 2 wherein the at least additive comprises: one of a catalyst, anadhesive, an adhesion promoter, a mold release agent, a flame retardant,a stabilizer, and a colorant.
 4. The semiconductor package of claim 1wherein the first film further comprises: a filler added to the firstcompound.
 5. The semiconductor package of claim 1 wherein the first filmis laminated onto said substrate layer.
 6. The semiconductor package ofclaim 1 wherein the first compound comprises: a rod-like liquidcrystalline component; an element selected from a group of oxygen,carbonyl, carboxyl, oxycarbonyl, and amine; and (CH₂)n, n being from 1to
 20. 7. The semiconductor package of claim 1 wherein the firstcompound comprises: a rod-like liquid crystalline component; first andsecond elements, each being independently selected from a group ofoxygen, carbonyl, carboxyl, oxycarbonyl, and amine; and (CH₂)n, n beingfrom 2 to
 20. 8. The semiconductor package of claim 1 wherein themultilayer is curable at a temperature.
 9. The semiconductor package ofclaim 8 wherein said temperature is above a melting point of one of thefirst and second compounds.
 10. A packaged semiconductor devicecomprising: a semiconductor die; a substrate layer; and a dielectriclayer disposed over the substrate layer said dielectric layer betweensaid semiconductor die and said substrate layer, the dielectric layercomprising: a first film formed from a first compound containing a firstliquid crystalline component, wherein the first liquid crystal componentof the first film is oriented in a first direction, and a second filmformed from a second compound comprising a second liquid crystallinecomponent, wherein the second liquid crystal component of the secondfilm is oriented in a second direction the second direction differentand not orthogonal to the first direction, the second film beingcombined with the first film to form a multilayer which produces acoefficient of thermal expansion (CTE) in the dielectric layer thatmatches a CTE of the substrate layer.
 11. The packaged semiconductordevice of claim 10 wherein the first film comprises: at least anadditive added to the compound.
 12. The packaged semiconductor device ofclaim 11 wherein the at least additive comprises: one of a catalyst, anadhesive, an adhesion promoter, a mold release agent, a flame retardant,a stabilizer, and a colorant.
 13. The packaged semiconductor device ofclaim 10 wherein the first film further comprises: a filler added to thefirst compound.
 14. The packaged semiconductor device of claim 10wherein the first film is laminated onto the substrate.
 15. The packagedsemiconductor device of claim 10 wherein the first compound comprises: arod-like liquid crystalline component; an element selected from a groupof oxygen, carbonyl, carboxyl, oxycarbonyl, and amine; and (CH₂)n, nbeing from 1 to
 20. 16. The packaged semiconductor device of claim 10wherein the first compound comprises: a rod-like liquid crystallinecomponent; first and second elements, each being independently selectedfrom a group of oxygen, carbonyl, carboxyl, oxycarbonyl, and amine; and(CH₂)n, n being from 2 to
 20. 17. The packaged semiconductor device ofclaim 10 wherein the multilayer is curable at a temperature.
 18. Thepackaged semiconductor device of claim 17 wherein said temperature isabove a melting point of one of the first and second compounds.